Analysis of the impact of hydrological alterations and multiple stress factors on the ecological status of Alpine freshwater ecosystems

Freshwater ecosystems are severely undergoing degradation due to the presence of multiple stressors that are undermining their biodiversity. In this sense, quantifying these effects on Alpine regions is challenging, due to the lack of tailored field measurements of hydrological, biological and chemical variables. This work aims to touch some of these aspects, with particular attention to hydrological dynamics and their effects on macroinvertebrates. Field activities have been conducted within the Adige catchment which has been selected as a case study in the FP7 project GLOBAQUA. Collected data have been analyzed by means of statistical tools and results showed a seasonal and spatial variability of biological communities related to hydrological and chemical variables. In particular, it has been observed that richness, diversity and relative composition of macroinvertebrates community are chiefly affected by hydrological alteration and urban pollution. Available literature confirmed that hydrological alteration is one of the most important factors affecting riverine ecosystems. In Alpine regions, most of the hydrological alterations observed are due to hydropower that represents the major source of energy in the Trentino-Alto Adige region. Since the introduction of the free energy market in Italy, hydropower production shows large fluctuations at the daily and larger temporal scales, as the managers aim at producing when the energy price is high. This increased the variability of streamflow downstream the restitution of the power plants. Changing climate is an additional stressor that can enhance the effects of these anthropogenic influences. Thereby, in this work hydrological alterations have been distinguished between those forced by climate change and those caused by the presence of hydropower plants and have been analysed in detail. The former have been analysed downstream of the Careser glacier, which has long-term observations of climatic variables, mass balances and streamflow. The main purpose of this study was finding a direct relationship linking biological indicators to streamflow variations related mainly to hydropower operations. Quantifying these effects is challenging due to the fact that the behaviour by which macroinvertebrates respond remains largely unexplained. However, analyses of similarities and independence, performed at the basin scale with data provided by the local Environmental Protection Agencies, showed evident differences in the biological communities between impacted and non-impacted sites. These results bring us to believe that a relationship between biological data and hydrological alteration is expected to exist, but that is not clearly explicated by simple correlations. Giving a quantitative interpretation of this correlation could help hydropower manager to improve and optimize the energy production with a more realistic scenario of the effects on the biological community, with also a perspective of the combined effects caused by the presence of multiple reservoirs within the basin.